1. Field of the Invention
The present invention relates to valves for automatically shutting off the flow of fluids in response to an emergency situation.
2. Description of the Prior Art
Natural gas is increasingly being used as a source of energy by both residential and commercial consumers due to its convenience, cleanliness, and efficiency. Natural gas can be used for heating, cooling, and cooking, and is quickly replacing oil and coal as the preferred energy source in many parts of the country. An important reason for its growth in popularity lies in the ease of delivery in which it can be supplied to a consumer. Instead of relying on periodic deliveries which can be hindered by inclement weather, gas is typically piped directly to the consumer. Most new communities are being constructed with the exclusive use of natural gas in mind, by installing extensive gas line networks to serve the current or future residents.
Despite the convenience of natural gas, it also presents a significant danger. Since natural gas is highly flammable, a rupture in the gas lines resulting in gas leakage can cause catastrophic damage to adjacent structures due to fires or explosions. Gas flowing in gas lines is susceptible to fluctuations in pressure due to the varying loads imposed on the gas line by the consumer, to leaks present in the lines, and other conditions beyond the control of the supplying utility. Due to these fluctuations, there have been instances where the pressure on a consumer's premises have been too low or too high for safe operation. A low pressure is dangerous because pilot lights or operating burners may become extinguished, which would result in gas filling the premises when the gas pressure again increases, thereby possibly causing an explosion or asphyxiation of the consumer. A high pressure is likewise dangerous because the equipment conveying and using the gas may break, thus placing the life and property of the consumer in jeopardy.
These dangers are most acute in areas of the country which experience periodic earthquakes or other seismic disturbances that cause buried pipelines to rupture. For example, a large percentage of homes during recent earthquakes in California and in Japan were consumed by fires started from leakage from ruptured gas lines. Earthquake preparedness experts caution all natural gas consumers to promptly close of all gas lines entering a structure shortly after experiencing an earthquake. By closing off gas lines, the amount of gas which could leak into the structure can be minimized, and the consequent risk of fire reduced.
Automatic shut-off valves which close off the gas line in response to a seismic disturbance are well known in the art. A common feature of many of such automatic valves is the use of a ball which can be dislodged by seismic disturbance and which falls into a valve seat position, thereby blocking flow through the valve structure. Example of such automatic shut-off valves are seen in U.S. Pat. No. 2,637,331, issued to Timothy J. Sullivan on May 5, 1953, and U.S. Pat. No. 5,209,252, issued to Cery B. Perle on May 11, 1993. U.S. Pat. No. 2,812,770, issued to Timothy J. Sullivan on Nov. 12, 1957, describes a solenoid operated safety cut-off valve having a pressure responsive diaphragm and a shock sensitive ball valve.
U.S. Pat. No. 5,209,454, issued to Paul D. Engdahl et al. on May 11, 1993, shows a safety shutoff valve having a pivoted flapper arm held in the open position by a permanent magnet embedded therein. When the magnetic attractive force is reduced enough, the arm swings down by gravity into the closed position. The magnetic attractive force is reduced by an opposing electromagnet or by mechanical displacement of a ferromagnetic ball.
Other automatic shut-off valves close off the gas line in response to a sudden increase or decrease in pressure in the gas line or in response to a failure of the electrical power supply. A common feature of such automatic shut-off valves is the use of a flexible diaphragm which responds to a sudden increase or decrease of pressure by moving to seal off the valve. Examples of such valves are seen in U.S. Pat. No. 2,620,820, issued to Paul L. Born on Dec. 9, 1952; U.S. Pat. No. 3,056,424, issued to Louis B. Courtot et al. on Oct. 2, 1962; and U.S. Pat. No. 3,842,858, issued to Frank E. Bobo on Oct. 22, 1974. U.S. Pat. No. 2,881,787, issued to Timothy J. Sullivan on Apr. 14, 1959, describes a safety control valve having two solenoid controlled pressure responsive diaphragms. The valve in its open position is responsive to low and high supply pressure and will automatically close upon variations thereof from a predetermined set level. In addition, the valve will automatically close upon failure of the electrical power supply.
Further examples of shut-off valves which close the gas line in response to failure of the power supply may be seen in U.S. Pat. No. 2,839,929, issued to Wilbur F. Hurlburt, Jr. on Jun. 24, 1958; U.S. Pat. No. 2,875,616, issued to George M. Marks on Mar. 3, 1959; and U.S. Pat. No. 3,259,357, issued to Karl F. Sharp on Jul. 5, 1966. Hurlburt shows a solenoid operated valve mechanism that includes a manual reset handle which can be tripped in response to a departure from a normal or predetermined condition, including power failure. Marks illustrates a solenoid controlled safety-cut off valve. When the solenoid is energized the valve is in the open position. Upon loss of power, the solenoid is deactivated and the valve is closed. Sharp shows an automatic shut-off valve having a latch element which is subject to positive impact force when circuit failure is detected. The impact force is supplied by an impact head powered by a spring which is released upon failure of the circuit.
However, none of the above referenced patents show an automatic safety shut-off system having a first valve including a sealing piston that is controlled by a pressure responsive locking mechanism which responds to above normal gas line pressure, a second valve responsive to lower than normal pressure downstream of the shut-off system, and a third valve responsive to interruption of electrical power supplied to machinery using fluid from the gas line.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.